#include<bits/stdc++.h>
using namespace std;
namespace IO{
    char buff[1<<21],*p1=buff,*p2=buff;
    char getch(){
        return p1==p2&&(p2=((p1=buff)+fread(buff,1,1<<21,stdin)),p1==p2)?EOF:*p1++;
    }
    template<typename T>
    void read(T &x){
        char ch=getch();int fl=1;x=0;
        while(ch>'9'||ch<'0'){if(ch=='-')fl=-1;ch=getch();}
        while(ch<='9'&&ch>='0'){x=x*10+ch-48;ch=getch();}
        x*=fl;
    }
    template<typename T,typename ...Args>
    void read(T &x,Args& ...args){
        read(x);read(args...);
    }
    char obuf[1<<21],*p3=obuf;
    void putch(char ch){
        if(p3-obuf<(1<<21))*p3++=ch;
        else fwrite(obuf,p3-obuf,1,stdout),p3=obuf,*p3++=ch;
    }
    char ch[100];
    template<typename T>
    void write(T x){
        if(!x)return putch('0');
        if(x<0)putch('-'),x*=-1;
        int top=0;
        while(x)ch[++top]=x%10+48,x/=10;
        while(top)putch(ch[top]),top--;
    }
    template<typename T,typename ...Args>
    void write(T x,Args ...args){
        write(x);write(args...);
    }
    void flush(){fwrite(obuf,p3-obuf,1,stdout);}
}
using namespace IO;
const int N=1e6+5,mod=1e9+7;
inline int Mod(int x){return x>=mod?x-mod:x;}
inline int poww(int x,int y){
    int sum=1;
    while(y){
        if(y&1)sum=1ll*sum*x%mod;
        x=1ll*x*x%mod;
        y>>=1;
    }
    return sum;
}
int n,k,ans;
int a[N];
int f[5];
signed main(){
    freopen("game.in","r",stdin);
    freopen("game.out","w",stdout);
    read(n,k);
    for(int i=1;i<=n;i++)read(a[i]);
    for(int i=1;i<=min(n-k,3);i++)f[i]=1;
    for(int i=n-k+1;i<=n;i++)
        for(int j=min(i,3);j>=1;j--)
            f[j]=Mod(1ll*(i-j)*f[j]%mod+1ll*(mod+j-3)*f[j-1]%mod);
    int tmp=1;
    for(int i=n-1;i>=n-k;i--)tmp=1ll*tmp*poww(i,mod-2)%mod;
    for(int i=1;i<=n;i++)ans=Mod(ans+1ll*a[i]*f[min(i,3)]%mod);
    write(1ll*ans*tmp%mod);
    flush();
    return 0;
}